It is now widely appreciated that heavy metals may have deleterious effects on living organisms. Because of the variety of the metals involved and the diversity of the effects, it is likely that a number of different mechanisms are involved. Recent studies have indicated that some heavy metals are mutagenic and that they may form physical complexes with DNA and chromatin. To learn more about the interaction of metal ions with DNA, we have begun by studying the effect of Hg2 plus and Ag plus on the buoyant density of synthetic DNA polymers of defined sequence. It is hoped that eventually such studies will be useful in elucidating the mechanism by which genetic alterations occur.